1. Field of the Invention
The present invention relates to the technology field of micro antenna, and more particularly to a multilayer chip antenna having internal capacitive loads.
2. Description of the Prior Art
Nowadays, communication products are designed to have light weight and compact size with the development of science and technology, such that the electronics devices or components must be miniaturized for integrated into the corresponding communication products. Antenna is an essential component for a wireless communication product, wherein planar inverted-F printed antenna (PIFA) is widely applied in various wireless communication products because having miniaturization characteristics.
Please refer to FIG. 1, which illustrates a framework view of a conventional planar inverted-F printed antenna. As FIG. 1 shows, conventionally-used planar inverted-F printed antenna 1a mainly consists of: a grounding layer 11a and a patch metal layer 12a, wherein the patch metal layer 12a is connected to the grounding layer 11a by a grounding portion 121a thereof. When applying the planar inverted-F printed antenna 1a, a feeding pin 122a is electrically connected to the patch metal layer 12a, so as to use the planar inverted-F printed antenna 1a to transceiver wireless signal. For example, the planar inverted-F printed antenna 1a is able to transceiver the wireless signal with 2.45 GHz frequency when the summation of length and width of the planar inverted-F printed antenna 1a is designed to 30 mm (i.e., one fourth (¼) of wavelength).
However, with the advancement of communication technology, the conventional planar inverted-F printed antenna 1a reveals some shortcomings and drawbacks in practical application. The shortcomings and drawbacks are as follows:    (1) It needs to pre-arrange an antenna installing region on the main board of the communication product (such as a cell phone) for facilitating the planar inverted-F printed antenna 1a be integrated onto the main board easily; however, the antenna installing region limits the miniaturization of the communication product;    (2) Moreover, since the transmission frequency characteristic of the inverted-F antenna 1a is dependent on the length and width summation of the patch metal layer 12a, it can easily know that the miniaturization of the inverted-F antenna 1a is bound to affect the antenna characteristics including transmission bandwidth and antenna efficiency.
In order to provide a solution for communication products' miniaturization, miniature antennas are developed and proposed. Please refer to FIG. 2, which illustrates a stereo view of a miniature cubic antenna. As FIG. 2 shows, the miniature cubic antenna 1′ disposed on an antenna installing region 20′ of a circuit board 2′ consists of: a cubic body 11′, a first conductive layer 12′, a signal transmitting layer 13′, a second conductive layer 14′, a signal feeding layer 15′, and a grounding layer 16′. In which, the conductive layer 12′, the signal transmitting layer 13′ and the second conductive layer 14′ are disposed on the top surface of the cubic body 11′, and the signal feeding layer 15′ is disposed on one side surface of the cubic body 11′ for connecting with the second conductive layer 14′.
As shown in FIG. 2, a large range of grounding electrode 22′ is arranged to surround the antenna installing region 20′. In addition, the grounding electrode 22′ has a connecting portion 221′ extending into the antenna installing region 20′ for connecting with the grounding layer 16′. Moreover, a signal feeding electrode 23′ is provided in the antenna installing region 20′, used for inputting signal into the signal feeding layer 15′ of the miniature cubic antenna 1′.
When applying the miniature cubic antenna 1′, an inductive effect would occur between the first conductive layer 12′ and the second conductive layer 14′, and the impedance bandwidth of the miniature cubic antenna 1′ for transmitting high-frequency signal is therefore increased due to the occurrence of the inductive effect. Simultaneously, a coupling capacitor would be produced between the grounding layer 16′ and the signal transmitting layer 13′, and the coupling capacitor facilitates the inductor produced between the first conductive layer 12′ and the second conductive layer 14′ electrically couple to the grounding electrode 22′ through the grounding layer 16′; therefore, the imaginary impedance of the inductor produced between the first conductive layer 12′ and the second conductive layer 14′ is eliminated.
Despite the miniature cubic antenna 1′ shows the advantages of high impedance bandwidth for transmitting high-frequency signal and being able to be miniaturized, inventors of the present invention find that the miniature cubic antenna 1′ still shows some shortcomings and drawbacks in practical application. The shortcomings and drawbacks are as follows:
(A) The miniature cubic antenna 1′ mainly uses the signal transmitting layer 13′ to transceiver wireless signal, so that any other conductive layers and/or electrodes cannot be disposed in the antenna installing region 20′. However, such prohibition limits the miniaturization of the communication product having the miniature cubic antenna 1′.
Thus, since both the conventionally-used planar inverted-F printed antenna 1a and miniature cubic antenna 1′ shows shortcomings and drawbacks in practical application, the inventors of the present application have made great efforts to make inventive research thereon and eventually provided a multilayer chip antenna having internal capacitive loads.